At this point it seems like everything should be ok other than the jet, the 65 would def be too rich with the stock pipe, probably with the country pipe too, specially without the case match. Since the main jet controlls the whole range on those (idle feeds through it iirc) could just be too rich to idle. When I first had 65cc polini not matched, 13.13, country pipe, and it was four stroking bad, it was definitely gutless. Can't hurt to try it.
Just to verify the idle jet you cleaned is the one in the bottom right pic on this page: http://www.zippymopedparts.com/partsviews.html
You also might want to take a look in to the intake and check how the cam lobe seals against the port inside the case. If you can see a gap the PO did not leave enough sealing surface around the port it could be leaking through there. Only other thing I can think of, You've went through the whole engine now, cleaned it up including the silicone gunk, and sealed it properly, should work.